DIY-WB Output Voltage Scaling

[Peter Gargano]

John Lamb wrote:
> 
> Are you saying that the Display has an embeded PIC that allows you to
> program a segmented curve fit?

Yes. The meter is calibrated for the Bosch LSM11 (0258104002) which
has a quite sharp transfer function like a NB sensor (but is apparently
manufactured to a higher tolerance than normal NB sensors).

The PIC could be reprogrammed for whatever Xfer function you want. As
the 16F84 is a flash device, it can be reprogrammed (up to 1000 times)
if you decide to change anything in the future.

The KC5300's display has 3 digits AND a BAR/DOT display (7 levels).
It would need to have a couple of component value changes and software
changes to work with the NTK sensor (LSM Vout is 0-1 Volt, but the
DIY Vout = 1.3-2.9 usable), but this is all quite doable. A small
deficiency is that there is no digital output so a nice addition
would be a serial interface for logging.

The MicroChip 16F84 does not have an A/D input, so the A/D converter
is kludged with a comparator and an integrated PWM output - uses just
two pins of the PIC (an 18 pin device). I'll scan the circuit soon and
provide some more info on how it could be modified.

Why not just use an LSM-11? I think the NTK sensor is a much nicer
device, and I'm not aware of Bosch trying to undercut NGK's price
and providing some competition in the WB sensor market. And this is
because there's a perception the a WB meter equals $$$$'s - a myth
I'm glad the DIY list is dispelling.

Peter.
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